/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.consensus.iot.logdispatcher;

import org.apache.commons.io.FileUtils;
import org.apache.iotdb.commons.utils.TestOnly;
import org.apache.iotdb.consensus.common.Peer;
import org.apache.iotdb.consensus.ratis.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.concurrent.ThreadSafe;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.util.Arrays;
import java.util.Optional;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * An index controller class to balance the performance degradation of frequent disk I/O.
 */
@ThreadSafe
public class IndexController {

    public static final String SEPARATOR = "-";

    private final Logger logger = LoggerFactory.getLogger(IndexController.class);

    private long lastFlushedIndex;
    private long currentIndex;

    private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

    private final String storageDir;

    private final Peer peer;
    private final String prefix;
    private final long initialIndex;

    private final long checkpointGap;

    public IndexController(String storageDir, Peer peer, long initialIndex, long checkpointGap) {
        this.storageDir = storageDir;
        this.peer = peer;
        this.prefix = peer.getNodeId() + SEPARATOR;
        this.checkpointGap = checkpointGap;
        this.initialIndex = initialIndex;
        // This is because we changed the name of the version file in version 1.0.1. In order to ensure
        // compatibility with version 1.0.0, we need to add this function. We will remove this function
        // in the future version 2.x.
        upgrade();
        restore();
    }

    public long updateAndGet(long index) {
        try {
            lock.writeLock().lock();
            long newCurrentIndex = Math.max(currentIndex, index);
            logger.debug(
                    "update index from currentIndex {} to {} for file prefix {} in {}",
                    currentIndex,
                    newCurrentIndex,
                    prefix,
                    storageDir);
            currentIndex = newCurrentIndex;
            checkPersist();
            return currentIndex;
        } finally {
            lock.writeLock().unlock();
        }
    }

    public long getCurrentIndex() {
        try {
            lock.readLock().lock();
            return currentIndex;
        } finally {
            lock.readLock().unlock();
        }
    }

    @TestOnly
    public long getLastFlushedIndex() {
        return lastFlushedIndex;
    }

    private void checkPersist() {
        if (currentIndex - lastFlushedIndex >= checkpointGap) {
            persist();
        }
    }

    private void persist() {
        long flushIndex = currentIndex - currentIndex % checkpointGap;
        File oldFile = new File(storageDir, prefix + lastFlushedIndex);
        File newFile = new File(storageDir, prefix + flushIndex);
        try {
            if (oldFile.exists()) {
                FileUtils.moveFile(oldFile, newFile);
                logger.info(
                        "version file updated, previous: {}, current: {}",
                        oldFile.getAbsolutePath(),
                        newFile.getAbsolutePath());
            } else {
                // In the normal state, this branch should not be triggered.
                // During the DataNode removing stage, the version file towards removing peer may be deleted
                // before all the async operations returns. We needn't add some sync operation here
                // because it won't infect the correctness
                logger.info(
                        "failed to flush sync index because previous version file {} does not exists. "
                                + "It may be caused by the target Peer is removed from current group. target file is {}",
                        oldFile.getAbsolutePath(),
                        newFile.getAbsolutePath());
            }

            lastFlushedIndex = flushIndex;
        } catch (IOException e) {
            logger.error("Error occurred when flushing next version", e);
        }
    }

    private void upgrade() {
        File directory = new File(storageDir);
        String oldPrefix = Utils.fromTEndPointToString(peer.getEndpoint()) + SEPARATOR;
        Optional.ofNullable(directory.listFiles((dir, name) -> name.startsWith(oldPrefix)))
                .ifPresent(
                        files ->
                                Arrays.stream(files)
                                        .forEach(
                                                oldFile -> {
                                                    String[] splits = oldFile.getName().split(SEPARATOR);
                                                    long fileVersion = Long.parseLong(splits[splits.length - 1]);
                                                    File newFile = new File(storageDir, prefix + fileVersion);
                                                    try {
                                                        logger.info(
                                                                "version file upgrade, previous: {}, current: {}",
                                                                oldFile.getAbsolutePath(),
                                                                newFile.getAbsolutePath());
                                                        FileUtils.moveFile(oldFile, newFile);
                                                    } catch (IOException e) {
                                                        logger.error("Error occurred when upgrading version file", e);
                                                    }
                                                }));
    }

    private void restore() {
        File directory = new File(storageDir);
        File[] versionFiles = directory.listFiles((dir, name) -> name.startsWith(prefix));
        File versionFile;
        if (versionFiles != null && versionFiles.length > 0) {
            long maxVersion = 0;
            int maxVersionIndex = 0;
            for (int i = 0; i < versionFiles.length; i++) {
                long fileVersion = Long.parseLong(versionFiles[i].getName().split(SEPARATOR)[1]);
                if (fileVersion > maxVersion) {
                    maxVersion = fileVersion;
                    maxVersionIndex = i;
                }
            }
            lastFlushedIndex = maxVersion;
            for (int i = 0; i < versionFiles.length; i++) {
                if (i != maxVersionIndex) {
                    try {
                        Files.delete(versionFiles[i].toPath());
                    } catch (IOException e) {
                        logger.error(
                                "Delete outdated version file {} failed", versionFiles[i].getAbsolutePath(), e);
                    }
                }
            }
            currentIndex = lastFlushedIndex;
        } else {
            currentIndex = initialIndex;
            versionFile = new File(directory, prefix + initialIndex);
            try {
                Files.createFile(versionFile.toPath());
                lastFlushedIndex = initialIndex;
            } catch (IOException e) {
                // TODO: (xingtanzjr) we need to handle the situation that file creation failed.
                //  Or the dispatcher won't run correctly
                logger.error("Error occurred when creating new file {}", versionFile.getAbsolutePath(), e);
            }
        }
    }

    public void cleanupVersionFiles() throws IOException {
        File directory = new File(storageDir);
        File[] versionFiles = directory.listFiles((dir, name) -> name.startsWith(prefix));
        if (versionFiles != null && versionFiles.length > 0) {
            for (File versionFile : versionFiles) {
                Files.delete(versionFile.toPath());
            }
        }
    }
}
